2022 Sun Climate Symposium – Abstracts - Laboratory for Atmospheric and Space Physics

2022 Sun Climate Symposium – Abstracts

Improved Climate-Record Reconstructions from Solar Variability and Earth System Observations

Welcome/Introduction – Overview of NASA Sun-climate Missions and Research Projects

Long-term Solar Irradiance Measurements and Continuity: The TSIS-1 & 2, CSIM, and CTIM Missions

Session 1

Recent Observation and Methods for Improving Climate Record Reconstructions

The 14C and tree-ring view of solar flares, cycles and climate

AJ Timothy Jull [jull@email.arizona.edu]^{1, 2}, Irina Panyushkina³, Chris Baisan³, Fusa Miyake⁴, Mihaly Molnár², Tamás Varga²

Department of Geosciences, University of Arizona, Tucson, AZ
Isotope Climatology and Environmental Research Center, Institute for Nuclear Research, Debrecen, Hungary
Laboratory for Tree-Ring Research, University of Arizona, Tucson, AZ
Institute for Space-Earth Environmental Research, Nagoya University, Nagoya, Japan

Excursions in the radiocarbon (14C) record are rapid changes which are caused by increases in the annual14C production rate in the atmosphere which are manifest by excesses of up to 20 ‰ in tree rings, caused by transient increases in the 14C production rate. This signal rises rapidly over a period of 1-2 yr and has a decay time of about 15-20 yr. These events are generally explained as a rapid increase of incoming cosmic rays or gamma rays. Only a few have been reproduced in multiple tree-ring records from many locations around the globe, particularly at ~660BCE, 774-775CE and 993-994CE. These excursions are positively connected to the impact of strong Solar Energetic Particles (SEP) events and are also observed from 10Be and 36Cl excursions in polar ice cores. Other proposed events show different structures and either coincide with Grand Solar Minima or other effects of a lesser magnitude. These include reported events at 815BCE, 5480BCE, 5410BCE, 1052/1054CE and 1279CE events. Changes in 14C production also need to be replicated and confirmed with additional tree rings as well as cosmic isotopes in ice cores. These excursions may be due to a mix of SEP and other astrophysical phenomena, such as gamma-ray bursts and geomagnetic excursions. We have developed new annual and sub-annual 14C datasets from tree rings from diverse geographical locations to confirm these phenomena. It appears that the intensity and structure of the 14C signal is multifaced, which complicates understanding of the forcing and attribution to the underlying astrophysical events. Timing of these events is important to register the recurrence intervals of these events for past and future 14C excursions. To test possible impacts on the chemistry and dynamics of atmosphere, we analyzed tree-ring reconstructed temperature anomalies at midlatitudes at subsequent years to the SEP & other events.

The Sunspot Number: Reevaluations and Reconstructions

We will quickly present the international effort that led to the first-ever revision of the Sunspot and Group Numbers (let us call them “the Sunspot Series”). The well-known Sunspot Number, for example, had never been revised extensively since its creation by Rudolf Wolf in 1849. We will review the different methods currently applied and envisioned for future versions of the two series (ISSI review paper, https://www.issibern.ch/teams/sunspotnoser/).

Since this first revision in 2015 (Solar Physics Topical Issue, 2016), the Sunspot Series have become living datasets that require constant monitoring since more source data are being recovered regularly (Arlt & Vaquero, 2020) and different stitching techniques are tested, the most recent one being a technique that, just as the ADF (Usoskin et al., 2016) does not require any temporal overlap between datasets, and uses tied ranking.

After this “small” review of previous efforts, we will focus more specifically on the reconstruction of the International Sunspot Number from raw sunspot data. With the team from ISSI, we are currently driving a large effort to gather raw data from all around the world. At the Royal Observatory of Belgium, within the WDC-SILSO (https://wwwbis.sidc.be/silso/) where the original Mittheilungen have been digitized (2017-2019) we also have 2 PhD students working on stitching historical and modern sunspot numbers and evaluating the quality of the reconstructed series through advanced statistical techniques. We will present the construction and its challenges.

The F10.7cm radio flux revisited

Frédéric Clette [frederic.clette@oma.be], World Data Center SILSO, Royal Observatory of Belgium

The F10.7cm radio flux is one of the primary long- term indices of solar activity. Beyond its solar physics applications, F10.7 is used as base proxy of the Sun’s UV irradiance for various ionospheric models and predictions. As it broadly extends the direct space- based measurements of the solar spectral irradiance, F10.7 thus plays a unique role in the understanding of the long-term Sun-Earth coupling.

By using the principles implemented for the re- calibration of the sunspot number (SN) series and by comparing the F10.7 series to the new upgraded SN version 2, we investigate the relation between those two global measures of solar activity, from 1947 to the present, and we verify a few key properties of the F10.7 long-term variations.

We find that:

the F10.7/SN relation is very closely linear, down to almost null activity
a low-range non-linearity of this relation appears for temporally-averaged values (monthly, yearly means). A data simulation shows that it is purely induced by the temporal smoothing, and that it varies with the width of the averaging.
the quiet-Sun F10.7 background flux depends on the duration of the quiet (spotless) intervals, ranging from 74 sfu for single-day intervals down to 67 sfu for the true “all-quiet” This reconciles the many seemingly incompatible values published until now.
an upward 10.5% scale jump occurs in the F10.7 series in 1980, cutting the full series into two halves, which are each fully homogeneous.

We conclude on the need to include a corresponding correction in all F10.7-based solar and geophysical applications spanning the entire length of the F10.7 record.

Ca II K observations for irradiance studies

Theodosios Chatzistergos [chatzistergos@mps.mpg.de],^1,2, N.A. Krivova¹, I Ermolli², K.L. Yeo¹, S, Mandal¹, S.K. Solanki¹, G. Kopp3, J-M. Malherbe^{5, 6}

Max Planck Institute for Solar System Research, Göttingen, Germany
INAF Osservatorio Astronomico di Roma, Porzio Catone, Italy
School of Space Research, Kyung Hee University, Republic of Korea
Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, CO
LESIA, Observatorie de Paris, France
PSL Research University, Paris, France

Solar irradiance has been measured since 1978 and was found to exhibit variations on all discernible timescales. Thus, monitoring solar irradiance is essential for assessing the influence of the Sun on Earth’s climate. The timeseries of direct measurements are, however, too short for this, and models are used to overcome this problem. By attributing the variations on time scales longer than about a day to the evolution of the solar surface magnetic field, models have been very successful in reconstructing the measured variability. But to account for the different contributions of surface magnetic features, such as sunspots and faculae, models require appropriated input data. Whereas direct sunspot data exist since the early 17th century, facular data are considerably scarcer. Therefore irradiance reconstructions prior to the period of direct measurements typically rely on sunspot data alone or on other indirect data of solar magnetism.

A largely unexplored source of facular data for irradiance studies is the collection of Ca II K observations, which extend back to 1892. The main reasons limiting their use have been a non-linear response of the photographic plates to sunlight and plentiful large-scale artefacts affecting the images. We will give on overview of the existing Ca II K archives along with the methods we have developed to perform their photometric calibration and to account for large-scale inhomogeneities allowing a reliable analysis of such data and their use for studies of past solar variability and irradiance. We will also present our recent efforts on reconstructions of irradiance variations from Ca II K data.

A stable reconstruction of total solar irradiance over the satellite era

Theodosios Chatzistergos [chatzistergos@mps.mpg.de],^1,2, N.A. Krivova¹, I Ermolli², K.L. Yeo¹, S, Mandal¹, S.K. Solanki¹, G. Kopp3, J-M. Malherbe^{5, 6}

Max Planck Institute for Solar System Research, Göttingen, Germany
INAF Osservatorio Astronomico di Roma, Porzio Catone, Italy
School of Space Research, Kyung Hee University, Republic of Korea
Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, CO
LESIA, Observatorie de Paris, France
PSL Research University, Paris, France

From the Latest TSI Measurements to the Historical Record

Greg Kopp [greg.kopp@lasp.colorado.edu]¹, Odele Coddington¹, Thierry Dudok de Wit², Karl Heuerman¹, Judith Lean¹, Brandon Stone¹, Lisa Upton³, Yi-Ming Wang⁴, Tom Woods¹

CU/LASP
University of Orléans
SSRC
NRL

The TSIS 1 mission’s Total Irradiance Monitor (TIM) is the newest spaceflight instrument measuring the total solar irradiance (TSI). It achieves superior absolute accuracy to any prior such instrument, helping mitigate potential data gaps in the uninterrupted, 43-year-long TSI climate data record. Direct overlap with the SORCE/TIM continues that mission’s 17-year record with this newer version of the TIM. Both show better inherent stabilities than any other flight TSI instrument, helping reduce uncertainties of long-term solar variability on climate- critical decadal timescales. To extend the space-era measurement records back in time, as needed for understanding natural influences on climate variability, a modeling-focused effort is underway to create an historical TSI reconstruction using updated results from the Advective Flux Transport model to simulate solar activity over the last 300 years based on the latest sunspot-number records and the NRLTSI proxy model.

Curious long-term increase of the visual band of the solar spectrum in TAV2 and TSIS-1 SIM datasets

Kalevi Mursula [kalevi.mursula@oulu.fi]¹, K. Teräsvuo², O. Coddington³, J. Harder³, T. Woods³

Space Climate Group, Space Physics and Astronomy Research Unity, University of Oulu, Oulu, Finland
Citizen scientist, Helsinki, Finland
Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, CO

Total solar irradiance (TSI) has been measured by satellites for more than four decades, which provides an estimate of the amount of TSI variation over this time interval. Satellite measurements have established the variation of TSI in phase with sunspots by roughly 1000 ppm. This variation has slightly decreased during the last decades, following the related decrease of sunspot cycle amplitudes. However, opposing results have been found for a longer-term trend of TSI between recent cycle minima. In addition to TSI, some composite sets have been constructed to cover mainly the high-frequency part of the spectrum over several decades. A number of spectral lines have been observed for more than a century, yielding information on the centennial evolution of limited parts of the solar spectrum. However, the full solar spectrum has been measured only for about 20 years, first by the SORCE satellite from 2003 until 2020 and, more recently, by the TSIS-1 satellite since 2018. These observations allow to study not only by how much the different parts of the spectrum contribute to the TSI, but also their temporal evolution during the last 20 years.

We use here the TSIS-1 SIM (version 7) data and the SORCE SIM TSIS-1 adjusted SSI values (version 2, TAV2) to study the temporal evolution of several bands of the solar spectrum. We note that, according to TAV2, the contribution of the visual band of the spectrum to TSI (vis-TSI) depicts a curious, almost systematic increase from the late declining phase of solar cycle 23, through the ascending to maximum phase of solar cycle 24. Vis-TSI increases by about 1000 ppm during this time, reaching its maximum in 2015, at the same time as TSI has its cycle maximum. However, the subsequent decrease of vis-TSI is relatively smaller than that of TSI, with vis-TSI remaining some 0.4W/m**2 higher during the sunspot minimum of 2018 than during the previous minimum. TSIS-1 observations since 2018 show the continuing increase of vis-TSI in the ascending phase of cycle 25 roughly at the same rate as in the ascending phase of cycle 24. These observations exclude a purely solar cycle related variation of vis-TSI and indicate a curious longer-term increase.

Session 2

Measurements and Models of Solar and Climate Variability

Historical drivers of climate change in the GISS Earth System Model

Gavin Schmidt [gavin.a.schmidt@nasa.gov]^1,Greg Falubegi, Larissa Nazarenko, David Rind, Drew Shindell, Tiehan Zhou

NASA Goddard Institute for Space Studies
Center for Climate System Research, Columbia University
Center for Climate System Research, Columbia University
NASA Goddard Institute for Space Studies (Emeritus)
Duke University
Center for Climate System Research, Columbia University

Climate models are improving in overall skill as they increase complexity. Full atmospheric chemistry, better tropospheric-stratospheric coupling, higher resolution, etc. are allowing for better representation of keys modes of variability such as the QBO, MJO and ENSO, and their teleconnections. The historical period (since 1850) has multiple important drivers of climate, including greenhouse gases, aerosols, ozone, volcanoes, land use, and of course, solar variability. Improvements in the robustness and availability of forcing datasets for TSI, spectral irradiance, solar energetic particles and cosmic rays allow for increasing completeness of solar activity forcing in the models. Attributions of short term (volcanic), decadal (solar) and long-term trends (greenhouse gases and aerosols) are all now clear. Our results confirm climate impacts over solar cycles in the stratosphere but impacts in the troposphere and surface are greatly affected by ocean-atmosphere coupling. Historical matches to temperatures and ozone observations are still impacted by the aliasing effects of volcanic aerosols.

The role of the polar vortex in Sun-Earth coupling

Lynn Harvey [lynn.harvey@lasp.colorado.edu], Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, CO

In the polar regions, the wintertime polar vortices play a critical role in both “bottom-up” atmospheric coupling via its modulation of planetary and gravity waves as well as “top-down” coupling via the transport of nitrogen oxides created by energetic particle precipitation. This talk will present the current state of understanding regarding the role of the polar vortex in coupling different atmospheric layers via both “bottom-up” and “top-down” processes. In particular, for “bottom-up” coupling, the polar vortices acts to vertically coupling the atmosphere from the ground to geospace by shaping the background wind field through which atmospheric waves propagate. For a variety of reasons, the geographic distribution of gravity wave (GW) activity depends on the strength and shape of the polar vortex. In the ionosphere, the frequency of occurrence of traveling ionospheric disturbances is linked to this GW activity and to polar vortex strength. For “top-down” coupling, energetic particle precipitation (EPP) generates nitrogen oxides (NOx=N+NO+NO2) in the mesosphere-lower thermosphere polar regions. In the wintertime, the polar vortices play a key role in downward coupling the thermosphere to the stratosphere by focusing the descent of EPP-NOx within its interior. State-of-the- art global climate models severely underestimate EPP- NOx transport during disturbed Arctic winters. Recent results demonstrate the role of Lagrangian Coherent Structures at mesopause altitudes in focusing the descent of EPP-NOx into the top of the polar vortex. Both upward and downward coupling processes will be elucidated by showing examples in observations and in whole atmosphere models. Outstanding questions and future directions will be discussed.

QBO/Solar modulation of the Madden-Julian short-term climate oscillarion: Mechanisms and comparisons with models

Lon Hood [lon@lpl.arizona.edu]¹, Thomas J. Galarneau, Jr.^{2, 3}, Natasha E. Trencham¹, C. Andrew Hoopes^{1, 4}

Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ
Cooperative Institute for Severe and High-Impact Weather Research and Operations, University of Oklahoma, Norman, OK
NOAA/OAR National Severe Storms Laboratory, Norman, OK
Hydrology and Atmospheric Sciences Dept., University of Arizona, Tucson, AZ

Recent work has shown that upper atmospheric conditions significantly modulate the occurrenc rate and amplitude of the Madden-Julian Oscillation (MJO), which is a tropical convective disturbance with important consequences for weather events at northern latitudes. Specifically, observations indicate a modulation of the MJO in northern winter by zonal winds in the equatorial and subtropical stratosphere driven by the quasi-biennial oscillation (QBO) and the 11-year solar cycle. The modulation is such that more strong MJO events occur during winter when the QBO is in its easterly phase (QBOE) and when the 11-year solar cycle is in its minimum phase (SMIN). Detailed studies of meteorological reanalyses show that a likely mechanism for both the QBO and solar modulations of the MJO is an increased occurrence of extratropical wave forcing events, including stratospheric warmings, in late fall and early winter under QBOE/SMIN conditions relative to QBOW/SMAX conditions. Currently, global climate models (GCMs) fail to simulate the QBO-MJO connection and it is also doubtful that they are able to simulate the solar- MJO connection. We are currently analyzing historical simulations from a series of GCMs with realistic QBOs and 11-year solar spectral irradiance forcing.

Results so far indicate that the increase in extratropical wave forcing in early winter that leads to reduced tropical lower stratospheric static stabilities in mid- winter during QBOE/SMIN is too weak relative to that which occurs observationally. Possible reasons for this deficiency will be discussed with an aim to improve model simulations of QBO/solar forcing of surface climate on both short and long time scales.

Observations of a Cooling and Contracting Mesosphere from 2002-2021

Lon Hood [lon@lpl.arizona.edu]¹, Thomas J. Galarneau, Jr.^{2, 3}, Natasha E. Trencham¹, C. Andrew Hoopes^{1, 4}

Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ
Cooperative Institute for Severe and High-Impact Weather Research and Operations, University of Oklahoma, Norman, OK
NOAA/OAR National Severe Storms Laboratory, Norman, OK
Hydrology and Atmospheric Sciences Dept., University of Arizona, Tucson, AZ

Non-Gaussian Distribution of TOA SW Flux as Observed by MISR and CERES

Jae Lee [jae.n.lee@nasa.gov]^1,2, Dong Wu¹

Joint Center for Earth Systems Technology, University of Maryland, Baltimore County, Baltimore, MD
NASA Goddard Space Flight Center, Greenbelt, MD

In this work, we describe the non-Gaussian probability density functions of top of the atmosphere (TOA) short-wave (SW) flux, in comparison of two satellite measurements and how the statistical third moments can impact the quantification of the globally averaged flux. Gaussian distributions are naturally assumed in atmospheric data analysis. This, however, is not always true for the TOA SW flux distribution. The probability density function (PDF) of the TOA SW flux is not normally distributed but positively skewed. In both observations, the global median value of the SW flux is ~3 W/m2 less than global mean, due to the positive skewness of the SW flux distribution. The global mean TOA SW flux converted from MISR is about 7 W/m2 (~7%) less than CERES measured flux during the last two decades. Surprisingly, Hemispheric asymmetry exists in the 1:30 PM local time TOA SW observations. SH reflects 3.92 W/m2 and 1.15 W/m2 more SW flux than NH, with MISR and CERES Single Scanner Footprint (SSF1deg) products, respectively. We can infer that the offsetting by afternoon clouds in the SH is greater than the effect of hemispheric imbalance of SW flux caused by different land masses in two hemispheres. While the characteristics of the two SW fluxes are agreeable with each other, differences in the regional PDF from two different SW fluxes are outstanding over high cloud regions and high altitude regions. Our analysis shows that some parts of the different skewness from two measurements may be attributed to different treatments between MISR and CERES for inaccurate corrections for the radiance anisotropy of high cloud scenes.An update on the Direct Influence of Solar Spectral Irradiance on the Surface Climate

Xianglei Huang [xianglei@umich.edu]¹, Xiuhong Chen¹, Dong L. Wu², Peter Pilewskie³, Odele Coddington³, Erik Richard³

1 Department of Climate and Space Sciences and Engineering, University of Michigan, Ann Arbor, Ann Arbor, MI

2 NASA Goddard Space Flight Center, Greenbelt, MD

3 Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, CO

Not only total solar irradiance (TSI) but also spectral solar irradiance (SSI) matter for our climate. Different surfaces can have different reflectivity for the visible (VIS) and near-infrared (NIR). Our recent study showed that the TSI observed by TSIS-1 differs from the counterpart used by the CMIP6 climate models by no more than 1 W m−2; however, the SSI difference in a given VIS (e.g., 0.44–0.63 μm) and NIR (e.g., 0.78–1.24 μm) band can be as large as 4 W m−2 with opposite signs. The study also employed the slab- ocean version of the NCAR CESM2 to understand to what extent such different VIS and NIR SSI partitions can affect the simulated climate. The results suggest that, even for the identical TSI, the surface albedo feedback can be triggered by different SSI partitions between the VIS and NIR. Here we reported an updated study on this using the fully coupled CESM2 model. Two sets of four-member ensemble runs have been run for 50 years. Compared to the slab-ocean runs, considering full ocean dynamics makes the impact of the VIS-NIR partition on Southern Oceans smaller but still discernible in the Arctic. Using the TSIS-1 observed SSI leads to colder surface temperature and larger sea ice extent than using the CMIP6 default SSI dataset. The responses in the fully coupled run are ~50% of counterparts in the slab- ocean runs. The results underscore the importance of continuously monitoring SSI and the use of correct SSI in climate simulations.

Solar Variability Results from the Solar Radiation and Climate Experiment (SORCE) Mission

Tom Woods [tom.woods@lasp.colorado.edu]¹, Jerald W. Harder¹, Greg Kopp¹, Martin Snow^{1. 2. 3}, Erik C. Richard¹, Odele Coddington¹, Peter Pilewskie¹

Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, CO
South African National Space Agency, Hermanus, South Africa
University of the Western Cape, Department of Physics and Astronomy, Bellville, South Africa

The NASA Solar Radiation and Climate Experiment (SORCE) operated from 2003 to 2020 to provide key climate-monitoring measurements of total solar irradiance (TSI) and solar spectral irradiance (SSI) in the X-ray ultraviolet (XUV: 0.1-30 nm), ultraviolet (UV: 120-400 nm), visible (VIS: 400-800 nm), and near infrared (NIR: 800-2400 nm). This 17-year mission made TSI and SSI observations during the declining phase of Solar Cycle 23, during all of Solar Cycle 24, and at the very beginning of Solar Cycle 25. We will present the SORCE solar variability results observed during Solar Cycles 23 and 24 and comparison of solar cycle minima levels in 2008-2009 and 2019-2020. The differences between these two minima are very small and are not significantly above the estimate of instrument stability over the 11-year period. For validation of the SORCE solar cycle variability results, they are compared with solar rotation variability results and irradiance model predictions. We also compare the SORCE results to those from the Total and Spectral Solar Irradiance Sensor (TSIS-1: 2018-present); there are notable differences for wavelengths longer than 1600 nm. The new SSI measurements with improved accuracy and stability by TSIS/SIM are anticipated to resolve most of the remaining differences. However, the low solar cycle 25 activity so far does not provide enough solar- cycle variability to accurately address those differences yet.

The updated VIRGO TSI time series

Wolfgang Finsterle [wolfgang@pmodwrc.ch], Jean-Philippe Montillet, PMOD/WRC, Davos Dorf, Switzerland

We present a new data driven approach to correct the PMO6/VIRGO TSI measurements for long- term instrument degradation and to update the VIRGO TSI time series. The new method and updated time series will be discussed and compared to previous versions and data records from other TSI experiments.

What Causes Total Solar Irradiance Changes During a Deep Solar Minimum

Sergey Marchenko [sergey.marchenko@ssaihq.com]^1,2, Judith L. Lean³, Matthew T. DeLand^1,

1 Science Systems and Applications, Inc, Lanham, MD

2 NASA Goddard Space Flight Center, Greenbelt, MD

What drives the small (~50-100 ppm, cf. >1000 ppm solar-cycle amplitudes) total solar irradiance (TSI) changes during a deep solar minimum, i.e., in practical absence of detectable sunspots and long-lasting active regions? We consider the epoch June-October 2008 and investigate abundant data sets (TSI from SORCE/TIM and SOHO/Virgo; various Mg II line- activity indices; EUV fluxes from STEREO A&B and SOHO/SEM; magnetograms from SOHO/MDI) to show that TSI closely follows the changes in the total magnetic flux of the sources with |B|>80 G. In particular, even during the extended (up to one month) periods with no detectable sunspots, regions with magnetic flux in the range 80 to 600 G nevertheless persist on the Sun’s disc. These sources comprise the populations of (a) short-living (<20 min), small-scale (predominantly a single 2-arcsecond MDI pixel), ~evenly distributed regions, and (b) on average, more extended (a few MDI pixels) and longer-living (140- 260 min median lifetimes) magnetic areas. We ascribe the latter to the ephemeral regions, finding them clustering on ~200 Mm scales. Preliminary analysis of the histogram distributions of magnetic flux regions in 2008 indicates that even during this deep solar minimum, total magnetic flux exceeds that defined by essentially invariant Gaussian distributions. This suggests that TSI during more extended, deep minima, such as the Maunder Minimum, may be lower than in 2008.

SOLSTICE: Seventeen Years, Eighteen Versions

Marty Snow [msnow@sansa.org.za]¹, W. McClintock², T. Woods², J. Elliott²

1 South African National Space Agency (SANSA)
2 Laboratory for Atmospheric and Space Physics (LASP)

The SOLar-STellar Irradiance Comparison Experiment (SOLSTICE) onboard the Solar Radiation and Climate Experiment (SORCE) made measurements of ultraviolet solar spectral irradiance (SSI) from 2003 to 2020. This seventeen year SSI record includes the decline of solar cycle 23 and the full solar cycle 24. We will present an overview of the in-flight calibration of SOLSTICE, and the solar variability results from the final data release (version 18). Absolute calibration results agree with the Total and Spectral Solar Irradiance Sensor (TSIS-1) within 5% throughout the 200-300 nm overlap region. Comparison to the SATIRE-S irradiance model shows good agreement up to 260 nm. The version 18 data products not only include improved calibration algorithms, but also include the full 0.1 nm spectral resolution and a high-cadence Lyman alpha product.

Understanding the variability of Balmer Lines

Serena Criscuoli [scriscuo@nso.edu]¹, Sergey Marchenko^2,3, Matthew DeLand ^2,3, Debi Prasad Choudhary^,4, and Greg Kopp ⁵

National Solar Observatory, Boulder, CO
Science Systems and Applications, Inc, Lanham, MD
NASA Goddard Space Flight Center (GSFC), Greenbelt, MD
Department of Physics and Astronomy, California State University, Northridge, CA
LASP / University of Colorado – Boulder

Balmer lines are fundamental astrophysical diagnostics. In particular, variations of stellar spectra in Hydrogen lines are used to study stellar chromospheric activity at different temporal scales, including flares and CMEs. However, recent studies have shown that the variability of Balmer indices derived from observations of F-G-K stars may deviate from the ones observed in other chromospheric indices as those derived from the MgII and the CaII lines. The Sun offers a means of exploring such measurements while also having the imaging capability to help discern the causes of observed spectral variations. Here, we investigate the variability of solar Balmer lines (H-α, -β, -γ, -δ) observed by OSIRIS, SCIAMACHY, OMI, and GOME-2 space-borne radiometers, combining these precise, long-term observations with abundant, high-resolution data from the ground-based NSO/ISS spectrograph. We relate the detected variability to the appearance of magnetic features on the solar disk. We find that on solar- rotational timescales, the Balmer line activity indices (defined as line-core to line-wing ratios) closely follow variations in the total solar irradiance (which is predominantly photospheric), thus frequently (specifically, during passages of sunspot groups) deviating from behavior of activity indices that track chromospheric activity levels. On longer timescales (years), the correlation with chromospheric indices increases, with periods of low- or even anti-correlation found at intermediate timescales.

Comparison of these observations with estimates from semi-empirical irradiance reconstructions allows to quantify the contributions of different quiet and magnetic features (i.e., network, plage, sunspots). We conclude that the observed complex relation between the variations of Balmer and other chromospheric indices most likely results from the lower sensitivity of Balmer lines to the network and plage components, and in part from the higher sensitivity to the passage of filaments.

Solar H alpha excess during Solar Cycle 24 from full-disk filtergrams of the Chromospheric Telescope

Andrea Diercke [adiercke@nso.edu]^{1, 2, 3}, C. Kuckein ^{2, 4, 5}, P.W. Cauley ⁶, K. Poppenhäger², J.D. Alvarado-Gómez², E. Dineva ^{2, 3}, C. Denker ²

National Solar Observatory (NSO), Boulder, CO
Leibniz Institute for Astrophysics Postdam (AIP), Postdam, Germany
University of Postdam, Institute for Physics and Astronomy, Postdam, Germany
Instituto de Astrofísica de Canarias (IAC), Tenerife, Spain
Departamento de Astrofisica, Universidad de La Laguna, Tenerife, Spain
Laboratory for Atmospheric and Space Physics (LASP), University of Colorado, Boulder, CO

The chromospheric H-alpha spectral line is a strong line in the spectrum of the Sun and other stars. In the stellar regime, this spectral line is already used as a powerful tracer of magnetic activity. For the Sun, other tracers are typically used to monitor solar activity. Nonetheless, the Sun is observed constantly in H-alpha with globally distributed ground-based full- disk imagers. The aim of this study is to introduce the imaging H-alpha excess and deficit as tracers of solar activity and compare them to other established tracers: the relative sunspot number, the F10.7 cm radio flux, and the Mg II index. We use observations of full-disk H-alpha filtergrams of the Chromospheric Telescope (ChroTel) and morphological image processing techniques to extract the imaging H-alpha excess and deficit, which are derived from the intensities above or below 10% of the median intensity in the filtergrams, respectively. These thresholds allow us to filter for bright features (plage regions) and dark absorption features (filaments and sunspots). The H-alpha deficit reflects the cyclic behavior of polar crown filaments and their disappearance shortly before the solar maximum. In addition, we investigate the mean intensity distribution for H-alpha excess regions for solar minimum and maximum and find that the shape of the distributions for solar minimum and maximum is very similar, but with different amplitudes.

Furthermore, we investigate whether the active region coverage fraction or the changing H-alpha excess in the active regions dominates time variability in solar H-alpha observations. The weak correlation between coverage fraction and mean intensity leaves us pessimistic that the degeneracy between these two quantities can be broken for modeling of unresolved stellar surfaces.

Sunspot Cycle 25: Early Indications, Long-term Implications

Scott McIntosh [mscott@ucar.edu], Robert J. Leamon

National Center for Atmospheric Research, University of Maryland Baltimore County

NASA/GSFC

We are now fully six months (post-terminator) into Sunspot Cycle 25 (SC25). We will discuss those early months, including the Hale Cycle terminator itself. We will explore the consequences of that transition on SC25, what what we might expect in the remainder of the decade (and cycle).

The Solar Cycle Clock: Prediction of F10.7, EUV Irradiance, and the Last X-flare of Solar Cycle 25

Robert Leamon [Robert.j.leamon@nasa.gov]^1,2, Scott W. McIntosh³

University of Maryland, Baltimore County
NASA GSFC
NCAR

The Sun’s variability is controlled by the progression and interaction of the magnetized systems that form the 22-year magnetic activity cycle (the “Hale Cycle”) as they march from their origin at ~55º latitude to the equator, over ~19 years. At the Lake Arrowhead meeting, we introduced the concept of “Terminators,” the endpoints of those activity bands’ progress, and a new, and more insightful, way of looking at timing solar cycles than counting spots. Rather than the canonical minimum number of sunspots, consider a precise date — when there is no more old cycle polarity flux left on the disk. Expressed in this way, a Terminator is the end of a Hale Magnetic Cycle. The Cycle 24 Terminator occurred in December 2021. Based on these Terminators, we construct a new solar cycle phase clock which maps all solar magnetic activity onto a single normalized epoch. If the Terminators appear at phase 0 * 2π, then solar polar field reversals occur at then solar polar field reversals occur at ~0.2 * 2π, and the geomagnetically quiet intervals centered around solar minimum, which start at 0.6 * 2π and end at the Terminator are thus 40 of the normalized cycle. These “pre-Terminators” show a radical reduction of complexity of active regions and (like the Terminators) are well approximated by the time when the solar radio flux, F10.7 = 90 sfu. We demonstrate that the vast majority, 96%, of all X-flares happen between the Terminator and pre-Terminator. Further, sunspot max amplitude, the aa geomagnetic index, and F10.7 and EUV spectral irradiance from a hot corona are all predictable from a normalized unit cycle from Terminator to Terminator.

Sunspot Group Numbers 1700-2021 with Monthly Resolution from Several Populations of Observations and Implications for Climate Change

Leif Svalgaard [leif@leif.org], Stanford University

We show that the observations of sunspots and their grouping into active regions fall into [at least] four distinct populations determined by discontinuities in observing technology and by evolving views of what constitutes active regions and their evolution. For each population daisy-chain-free ‘backbones’ with monthly resolution can be constructed and linked together to form a dataset for the years 1700-2021. The populations have different statistical properties that do not carry over from one population to the next. The solar observations are supported by several well- understood proxies. An important conclusion is that there is no [upwards] long-term trend in solar activity over the past three centuries with obvious implications for the causes of climate change over the same period.

Session 3

Long Term Atmospheric Measurements

Tracking Changes in Earth’s Energy Flows

The influence of Clouds on Solar Radiation in the “New Arctic”

Growing use of Satellites for Supporting Solar Energy Applications

Time Series Analysis of the NASA MODIS and VIIRS Cloud Products

Satellite Hyperspectral Infrared Climate Time Series Combining AIRS and CrIS

Inferring Three Decades of Global Cloud and Moisture Properties from the HIRS Data Record

Evolution of Stratospheric Temperature Trends from MW+IR Sounders, GPS-RO and Reanalysis using Nonparametrics Multivariate Regression Techniques

Polar Mesospheric Clouds and Solar Effects: An update

Nitric Oxide Concentrations and Radiative Cooling in Earth’s Atmosphere Derived from SABER

The Essential Role of Photosynthesis in Defining Net Zero Carbon Dioxide Emissions for Equilibrium Calculations

Multidecadal Northern Hemisphere Midlatitude Geocoronal Hydrogen Emission Observations

Session 4

Solar Influence on the Atmosphere and Climate

The Active Sun and its Impact on the Early Earth Climate

Vladimir Airapetian [Vladimir.airapetian@nasa.gov], NASA GSFC/SEEC and American University, Washington, DC

Understanding the climate conditions that allowed for the emergence of life on early Earth, and whether other inner planets in our Solar System possibly also supported habitable conditions early in their histories is central for answering the question: Are we alone? To answer this fundamental question, we need to know whether Earth could be a special outlier, or it could be a typical rocky planet. What role did the young Sun play in supporting the basic requirements for life as we know it such including persistent external energy fluxes, liquid water and organic compounds that promoted the emergence and complexication of biological systems on early Earth? Here I will describe how interdisciplinary research methodologies and tools of heliophysics, astrophysics, planetary and Earth science can be applied to address this complex question. Specifically, I will show how recent data from the Hubble and Kepler Space Telescopes opened a new avenue in reconstructing the life of the young Sun using observationally constraining state-of-the-art theoretical models of the coronal and wind environments young solar-like stars. I will then discuss how the data constrained energy fluxes from the young Sun including X-ray, and Extreme UV (XUV) emission, wind and frequent superflares impacted the magnetosphere, ionosphere, thermosphere and the lower atmosphere of early Earth. I will describe our recent atmospheric chemistry models impacted by superflares, coronal mass ejection and associated solar energetic particles (SEPs) from the young Sun. As high-energy particles penetrate the N2 – CO2 rich early Earth’s atmosphere, they produce dissociation, excitation and ionization of atmospheric species driving a chain of chemical reactions forming precursor of life molecules and nitrous oxide, a potent greenhouse gas. I will then highlight the results of our experiments on proton irradiation of simulated primitive mildly reducing Earth atmosphere to study the impact of SEPs, and analysis of products including N2O and amino acids. Finally, I will discuss the results of the 3D general circulation model, ROCKE- 3D of the early Earth with the atmospheric mixing ratios of nitrous oxide moderated by hard-spectrum SEP events from the young Sun and their implications for searching for habitable worlds.

Magnetic Variability of Sun-like Stars Observed by Kepler and TESS

Benjamin Montet[b.montet@unsw.edu.au], School of Physics, University of NewSouth Wales, Sydney, Austrailia

The Kepler and TESS missions have measured the brightness of millions of stars thousands of times. These observations provide opportunities to understand stellar variability on timescales from a few seconds to more than a decade. From stellar flares, to the growth and decay of starspots and facular networks, to potential magnetic activity cycles, these data enable us to contextualise Solar variability and understand the magnetic evolution of Sun-like stars across billions of years. In this talk, I will present an overview of how we can measure brightness variations on multiple timescales from these data, what they tell us about Sun-like stars and their planets at a variety of ages, and what questions we may be able to answer about magnetic activity on Solar analogs in the coming years. I will focus on variability observed over multi- year timescales and attempts to measure stellar activity cycles on stars similar to the Sun, and what these stars do and do not have in common with our own star.

Why active Suns are spot dominated

Nina-Elisabeth Nemec [nemec@mps.mpg.de]^1,2, A.I. Shapiro², E. Isik³, K. Sowmya², S.K. Solanki^2,4, R.H. Cameron², N.A. Krivova², L. Gizon^1,2,5

Institut für Astrophysik, Georg-August-Universität Göttingen, Göttingen, Germany
Max-Planck-Institut für Sonnensystemforschung, Justus-von-Liebig-Weg, Göttingen, Germany
of Computer Science, Turkish-German University, Istanbul, Turkey
School of Space Research, Kyung Hee University, Korea
Center for Space Science, NYUAD Institute, New York University Abu Dhabi, Abu Dhabi, UAE

Surfaces of the Sun and other cool stars are filled with magnetic fields, which are present in the form of dark spots or more diffuse bright structures (faculae). Both hamper detection and characterisation of exoplanets, affecting stellar brightness, spectra, as well as transmission spectra.

While stellar observations of the distribution of spot areas are unreliable and facular areas cannot yet be measured, observations of the solar spot and faculae disc coverages spanning several decades are available. This data revealed that with increasing spot coverage (hence activity level) the faculae coverage increases less rapidly, leading to a decrease in the facular-to- spot area ratios with increasing activity level. In an attempt to pinpoint the physical mechanism behind this peculiar behaviour, we employ a surface flux transport model (SFTM) to investigate the dependence of the facular on spot coverage for stars with varying activity levels. We first reproduce the observed solar trends of decreasing facular-to-spot ratio. We then proceed to extend our model to more active stars by gradually filling the stellar surface with more and more magnetic flux. We use the distributions of magnetic features to calculate the stellar photometric variability in the routinely used Strömgren b+y passband and the stellar chromospheric emission in the Ca II H\&K lines. This allows us to directly compare to stellar observations and test the established trends. Our model explains the observed switch from facula-dominated (e.g. observed for the Sun) to spot dominated variability on the cycle timescale for higher activity levels. We find that the diffuse magnetic flux associated with faculae exhibits a higher chance of encounters of opposite- polarity fields, leading to flux cancellation. This gradually leads to a decrease of the fractional facular area, resulting in spot domination.

Additionally, we are able to extend our model to different inclinations and metallicities to further understand, the importance of both faculae and spots to stellar activity and disentangling the signal of planets from the stellar signal.

The solar-stellar connection

Alexander Shapiro [shapiroa@mps.mpg.de], Max-Planck Institute for Solar System Research

The Sun is the only star where we can resolve the spatial scales on which fundamental processes take place. As a result it provides a perfect test bench for understanding the conditions in stellar atmospheres. Benefiting from the enormous recent progress in solar observations and models it is now possible to extend the models originally developed for and tested against the Sun to model stellar atmospheres. At the same time, modelling of stellar atmospheres becomes very timely since stellar observational data (e.g. obtained by Kepler and TESS space telescopes and Gaia space observatory) have emphasized the needs for developing methods for extracting information about solar-like stars and their planets from the available photometric and spectroscopic records. I discuss the recent advances in modelling stellar atmospheres brought by the solar know-how and show how studies of solar-stellar connection can be simultaneously beneficial for solar and stellar physics.

Inclinatin and metallicity dependence of the near-UV Ca II H\&K line emissions

Sowmya Krishnamurthy [krishnamurthy@mps.mpg.de]¹ , V. Witzke¹, S. Saar², A.I. Shapiro¹, N.E. Nemec ^3,1, T. Chatzistergos^1,4, K.L. Yeo¹, N.A. Krivova¹, S. K. Solanki^1,5

Max-Planck Institut für Sonnensystemforschung, Justus-von-Liebig, Göttingen, Germany
Harvard-Smithsonian Center for Astrophysics, Cambridge, MA
Institut für Astrophysik, Georg-August-Universität Göttingen, Göttingen, Germany
INAF Osservatorio Astronomico di Roma, Monte Porzio Catone, Italy
School of Space Research, Kyung Hee University, Korea

The emission in the near ultraviolet Ca\,{\sc ii} H \& K lines is modulated by the magnetic activity of a star. Although this emission has been serving as a prime proxy of magnetic activity for several decades, many aspects of the complex relation between stellar magnetism and Ca\,{\sc ii} H \& K emission are still unclear. In particular, it was suspected that Ca\,{\sc ii} H \& K emission might be also affected by the inclination of the star’s rotation axis and stellar metallicity. However, until now such effects on the S- index have remained largely unexplored. In order to fill in this gap we developed a physics-based model of Ca\,{\sc ii} H \& K emission which enables us to study such dependencies. We first tested this model for the case of the Sun, making use of the distributions of the solar magnetic features derived from observations together with the Ca\,{\sc ii} spectra synthesized with a non-LTE radiative transfer code. Its performance is validated by successfully reconstructing the observed variations of Ca\,{\sc ii} emission across four solar activity cycles.

Using the surface flux transport model, we simulated the distribution of magnetic features on the visible disk of solar-like stars at different inclinations over a period of 300 years. Combining this with the Ca\,{\sc ii} spectra for different metallicities, we obtained time-series of the S-index and investigated the effects of stellar inclination and metallicity. We show that the solar S-index values obtained by an out-of-ecliptic observer are different from those obtained by an ecliptic-bound observer. We find that depending on the inclination and period of observations, the activity cycle in solar S-index can appear weaker or stronger than in stars with a solar-like level of magnetic activity, showing that the solar S-index cycle is absolutely normal in the context of stars with near- solar magnetic activity. Further, we demonstrate that the changes in the atmospheric structure and Ca\,{\sc ii} line formation caused by increasing metallicity leads to a decrease in the S-index. We show that the modelled dependence agrees well with the observed dependence of S-index on stellar metallicity for a sample of solar-like stars, and propose a way to correct the metallicity dependence of S-index.

Session 5

Next-generation Observations and Models for Sun and Earth

The PREFIRE Mission: Documenting the Spectral Character of Polar Emission

Tristan L’Ecuyer [tristan@aos.wisc.edu]¹, Brian Drouin^,2, Brian Kahn², Nicole-Jeanne Schlegel², Sharmila Padmanabhan², Aronne Merrelli³, Xianglei Huang³, Jennifer Kay⁴, Nathaniel Miller¹

Department of Atmospheric and Oceanic Sciences, University of Wisconsin-Madison, Madison, WI
Jet Propulsion Laboratory, California, Institute of Technology, Pasadena, CA
Department of Climate & Space Science, University of Michigan, Ann Arbor, MI
Atmospheric and Oceanic Sciences, University of Colorado, Boulder, CO

The lack of consensus in predicted rates of Arctic warming, sea ice decline, and ice sheet melt in current climate models may be attributed, at least in part, to the lack of observational constraints on thermal fluxes and the atmospheric and surface properties that modulate them. For example, the spectral character of thermal emission at the surface and top of atmosphere at wavelengths longer than 15 microns has not been systematically observed. These far infrared wavelengths account for up to two-thirds of polar emission and carry unique spectral signatures of polar surfaces, ice clouds, and water vapor in cold environments. As a result, the far infrared observing gap introduces uncertainty in both satellite- and reanalysis-based reconstructions of the polar energy budgets that likely have substantial implications for predicting changes in sea ice cover, precipitation, ice sheet dynamics, and surface mass balance. The NASA Earth Ventures Instrument-4 (EVI-4) Polar Radiant Energy in the Far Infrared Experiment (PREFIRE) aims to reduce these uncertainties by documenting the spatial and temporal variations in spectrally-resolved far-infrared fluxes globally. Through the use of new ambient temperature detectors capable of making high-quality measurements up to 50 microns, PREFIRE observations will cover more than 95% the energetically-relevant portion of the infrared spectrum including wavelengths longer than 15 microns that have never been systematically observed from space. Estimates of spectral surface emissivity, water vapor, cloud properties, and the atmospheric greenhouse effect derived from these measurements offer the potential to advance models of thermal fluxes in the cold dry conditions characteristic of the polar regions and upper troposphere.

Observing Earth’s energy balance in the era of the Atmospheric Observing System (AOS)

Graeme Stephens [Graeme.stephens@jpl.nasa.gov], Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA

This talk considers the evolution of the satellite observational record of Earth energy balance leading to the next generation of observations that is in part represented by the Libera mission. The talk will outline the motivations for the next steps in Earth’s radiation budget observations calling out approaches that offer both greater spatial and spectral information about radiation fluxes than currently available. A review of the approaches proposed for EarthCARE, PREFIRE and AOS, all planned for the present decade, will be outlined. The importance of greater spectral information in Earth’s radiation budge than is currently available will be underscored.

Future Observations of Earth’s Radiation budget and the science they enable

Maria Hakuba [maria.z.hakuba@jpl.nasa.gov]¹, Peter Pilewskie², Graeme Stephens¹, and the Libera science team

Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA
Laboratory for Atmospheric and Space Physics & Department of Atmospheric and Oceanic Sciences, University of Colorado, Boulder, CO

This presentation will cover multiple aspects of Earth Radiation Budget (ERB) research and novel ERB observations. First, we will talk about the science goals and objectives of Libera, the recently selected EVC-1 mission. As one of its main goals, Libera aims to provide continuity ERB observations through measuring the broadband shortwave, longwave and total radiances with almost identical characteristics as the Clouds and Earth’s Radiant Energy System (CERES) instruments. Not only does Libera enable critical continuity of the 40-year radiation flux record, but introduces innovative technology to enhance scientific merit and to meet the future needs of smaller and cost-effective observation systems. Libera addresses the need to miniaturize radiometers but also the coincident imager retrievals required for the radiance-to-irradiance conversion. A novel “split- shortwave” radiometer will enable us to split the shortwave spectrum into nearly identical halves, one that is absorbed by the atmosphere while the other is not – the near-infrared and visible portions of solar radiation. Research possibilities are various with this novel measurement and, for example, will help us to advance the understanding of mechanisms that yield hemispheric symmetry in Earth’s albedo. Secondly, I will discuss different approaches to measure and estimate Earth’s energy imbalance (EEI) including the assessment of contemporary sea level budget using altimetry and GRACE/GRACE-FO observations.

Looking into the future, we will present ideas for a potential observing system that measures radiation pressure variations in orbit around Earth, which are proportional to the radiation fluxes entering and exiting our climate system. Initial feasibility simulations are under way to give evidence that this approach may indeed facilitate a high-accuracy measurement of TOA net radiative flux and EEI.

Libera and Continuity of the Earth Radiation Budget Climate Data Record

Peter Pilewskie [peter.pilewskie@lasp.colorado.edu], Maria Hakuba and the Libera Science Team, Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, CO and Jet Propulsion Laboratory, Pasadena, CA

The Libera Mission, named for the daughter of Ceres in Roman mythology, will provide continuity of the Clouds and the Earth’s Radiant Energy System (CERES) Earth radiation budget (ERB) observations from space. Libera’s attributes enable a seamless extension of the ERB climate data record. Libera will acquire integrated radiance over the CERES FM6- heritage broad spectral bands in the shortwave (0.3 to 5 μm), longwave (5 to 50 μm) and total (0.3 to beyond 100 μm) and adds a split-shortwave band (0.7 to 5 μm) to provide deeper insight into shortwave energy deposition. Libera leverages advanced detector technologies using vertically aligned carbon nanotubes with closed-loop electrical substitution radiometry to achieve radiometric uncertainty of approximately 0.2%. Libera will also employ a wide field-of-view camera to provide scene context and explore pathways for separating future ERB missions from complex imagers.

The Libera science objectives associated with continuity and extension of the ERB data record are to identify and quantify processes responsible for ERB variability on various times scales. Beyond data continuity, Libera’s new and enhanced observational capabilities will advance our understanding of spatiotemporal variations of radiative energy flow in the visible and near-infrared spectral regions. They will also enable the rapid development of angular distribution models to facilitate near-IR and visible radiance-to-irradiance conversion.

IR Measurements for CLARREO: the Compelling Need for an On-orbit SI Reference Sensor

Hank Revercomb [hankr@ssec.wisc.edu], Fred Best, Joe Taylor, Dove Tobin, Jon Gero, Bob Knuteson, University of Wisconsin-Madison, Space Science and Engineering Center (SSEC), Madison, WI

The higher accuracy possible from an SI reference sensor will, for the first time, provide radiative information about differences at the scale of the Earth radiative imbalance, 1 W/m2. As a result, it will allow significant climate changes to be resolved and assessed much sooner. The flight of a single, high quality, reference sensor of the type defined for the NASA Climate Absolute Radiance and Reflectivity Observatory (CLARREO) program would allow the international fleet of IR sounders to be inter-calibrated and used to establish an initial climate benchmark for future mission comparisons.

CLARREO IR spectrometer requirements for the emission spectrum (3.7-50 microns) have been met by the UW-SSEC Absolute Radiance interferometer (ARI) Engineering Model, demonstrating better than 0.1 K 3-sigma brightness temperature measurement accuracy (Taylor et al.. 2020). A key aspect of the ARI instrument is the On-orbit Verification and Test System (OVTS) for verifying its accuracy by reference to International Standards (SI). The OVTS includes a high emissivity cavity blackbody that can be operated over a wide range of temperatures to directly verify ARI calibration on orbit. Three small phase change cells are used to establish the fundamental temperature scale to better than 10 mK, real time.

The highest practical accuracy is needed as soon as possible for monitoring international progress towards achieving the purpose of the Paris Climate Agreement and other long-term goals.

CLARREO Pathfinder: A New Perspective of Earth

Yolanda Shea [Yolanda.shea@nasa.gov]¹, Peter Pilewskie², Paul Smith², Greg Kopp², Rajendra Bhatt¹, Constantine Lukashin¹, Gary Fleming¹

NASA Langley Research Center, Hampton, VA
Laboratory for Atmospheric and Space Physics, Boulder, CO

The Climate Absolute Radiance and Refractivity Observatory (CLARREO) Pathfinder mission will take spectral reflectance measurements of Earth from the International Space Station (ISS) with unprecedented accuracy. The CPF instrument, the Hyperspectral Imager for Climate Science (HySICS), will provide a novel view of Earth with its unique combination of measurement capabilities: unprecedented radiometric uncertainty of 0.3% (k=1) in reflectance, spectral range of 350-2300 nm, spectral resolution of less than 6 nm, and spatial sampling of approximately 0.5 km at nadir. The high accuracy of HySICS will be achieved using a novel approach to on-orbit calibration. In addition to the two primary science objectives to take high accuracy reflectance measurements and intercalibrate CERES and VIIRS, CPF measurements will enable a wide range of science applications. These additional applications were explored during a recent science workshop hosted by the CPF team. Invited and contributed formal and lightning talks were given by scientists from across the scientific community that discussed how CPF data could support or enhance their research. We will present an overview of the CLARREO Pathfinder mission’s current status and an overview of the CPF Science Workshop.

ARCSTONE: Providing a Spectral Irradiance Reference for On-Orbit Calibrations of Earth Monitoring Instruments

Greg Kopp [greg.kopp@lasp.colorado.edu]¹, Seth Cousin¹, Trevor Jackson², Costy Lukashin², Paul Smith¹, Tom Stone³

CU/LASP
NASA/LaRC
USGS

The ARCSTONE is a 6 U CubeSat funded by NASA’s Earth Science Technology Office’s Instrument Incubator and InVEST programs to provide a lunar- irradiance reference spectrum in the solar-reflected spectral range for improved calibrations and inter- calibrations of almost all on-orbit, Earth-monitoring instruments. The Moon, having similar radiance levels to Earth scenes and a surface stable to < 10 8 per year, provides a means of safely calibrating on-orbit Earth- viewing instruments able to point to it. Many Earth- monitoring instruments do exactly that to determine long-term relative stability corrections to account for on-orbit degradation. Absolute lunar-irradiance calibration uncertainties, using several years of ground-based measurements consolidated into the Robotic Lunar Observatory (ROLO) model, are at 5 to 10 % levels, although relative changes due to lunar phase and libration are known much better and can be calculated as a function of wavelength via the ROLO model for any recent time. The ARCSTONE flight instrument intends to lower the absolute lunar- irradiance uncertainties to the 0.5 % level for the 350 to 2300 nm spectral range and incorporate those improvements into the ROLO model, which will then allow calibration improvements to current, historical, and future Earth-monitoring instruments that have viewed or will view the Moon. The ARCSTONE InVEST program began in 2021 with planned launch in 2024.

TSIS-2 Development

Susan Breon [susan.r.breon@nasa.gov], NASA Goddard Space Flight Center

The Total and Spectral solar Irradiance Sensor – 2 (TSIS-2) is a project under development by NASA to provide continuity with TSIS-1 in the measurement of total and spectral solar irradiance. TSIS-2 has two instruments, the Total Irradiance Monitor (TIM) and Spectral Irradiance Monitor (SIM), which are being developed by the Laboratory for Atmospheric and Space Physics (LASP). The spacecraft is being developed by General Atomics – Electromagnetic Systems (GA). The paper describes the design of the TSIS-2 satellite and the plans for on-orbit operations.

Observation implementation lessons learned and the effect of the global pandemic on future strategies

Thomas Sparn [tom.sparn@lasp.colorado.edu], Laboratory for Atmospheric and Space Physics, Boulder, CO

This talk will discuss the pros and cons of the many past strategies used for solar irradiance measurement capture and the evolution history to insure data continuity. Evaluation and lessons learned from the global pandemic on current and future implementation of space systems data acquisition with emphasis on the TSI and SSI data records. The presentation will discuss how the growing polarization of the United States political environment may impact future implementations and possible strategies to help mitigate risk to data continuity.

Session 6

Improved Solar Reference Spectra: Implications for Remote Sensing and Radiative Transfer

The Full Spectrum Extension of the TSIS-1 Hybrid Solar Reference and Impacts for Solar Irradiance Variability Modeling

Odele Coddington [Odele.coddington@lasp.colorado.edu]¹, Erik Richard¹, Judith Lean¹, Dave Harber¹, Peter Pilewskie ^1,2, Tom Woods¹, Marty Snow ^{1, 3, 4}, Kelly Chance⁵, Xiong Liu⁵, Kang Sun⁵

Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, CO
University of Colorado Boulder, Department of Atmospheric and Oceanic Science, Boulder, CO
South African National Space Agency, South Africa
University of the Western Capte, Department of Physics and Astronomy, South Africa
Harvard-Smithsonian Center for Astrophysics, Cambridge, MA
University at Buffalo, Research in Energy, Environment and Water (RENEW) Institute, Buffalo, NY

Solar irradiance reference spectra are utilized by a wide variety of Earth science applications. For example, some trace gas retrievals from hyperspectral observations of ultraviolet and visible radiation require a well-calibrated, solar reference spectrum for wavelength alignment that is of even higher resolution than the observations themselves. Still other applications, such as solar irradiance variability modeling, require a solar reference spectrum that spans from the ultraviolet to the longwave infrared. The new, publicly-available, Total and Spectral Solar Irradiance Sensor (TSIS-1) Hybrid Solar Reference Spectrum (HSRS) has the spectral range (0.202 um to 2.73 um), spectral resolution (0.01 nm or better) and high accuracy across the spectrum (uncertainties of 0.3% between 0.4 and 2.365 um and 1.3% at wavelengths outside that range) to provide an important new constraint for Earth science applications. Motivation for the development of the TSIS-1 HSRS came from demonstrated differences in solar spectral irradiance observations by the TSIS-1 Spectral Irradiance Monitor and the CubeSat Compact Spectral Irradiance Monitor (CSIM) with other commonly used solar reference spectra that reached 8%, particularly in the near-infrared portion of the spectrum.

In this work, we will discuss the TSIS-1 HSRS and recent efforts to extend the spectral range to the full spectrum (0.115 um to 200 um) using direct measurements where possible and theoretical understanding in spectral regions where no measurements exist. Thus, the spectral range of the extended TSIS-1 HSRS encompasses an integrated energy in excess of 99.99% of the total solar irradiance and is therefore sufficient for Earth energy budget and climate studies. Then, we will discuss the planned adaptation of this extended TSIS-1 HSRS into a new version of the Naval Research Laboratory (NRL) solar spectral irradiance (SSI) variability model that is under development. The NRLSSI models have long heritage in various Earth science studies including renewable energy research, climate studies and climate assessment reports. Ultimately, the new version of the NRLSSI model, will also be released as version 3 of the National Centers for Environmental Information (NCEI) Solar Irradiance Climate Data Record (CDR), thereby transitioning improvements in understanding of the magnitude and variability of solar irradiance to the Earth science community.

The impact on model state of implementing the TSIS-1 Hybrid Solar Reference and Impacts for Solar Irradiance Variability Modeling

Daniel Marsh [marsh@ucar.edu]^1,2, Odele Coddington³

National Center for Atmospheric Research, Boulder, CO
Faculty of Engineering and Physical Sciences, University of Leeds, Leeds, UK
Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, CO

A new, daily record of solar spectral irradiance (SSI) commenced in 2018 with the Spectral Irradiance Monitor (SIM) on the Total and Spectral Solar Irradiance Sensor (TSIS-1) mission. The TSIS-1 SIM has technological advances in precision, accuracy and stability providing a superior SSI dataset than was obtained by the heritage SIM instrument on the SOlar Radiation and Climate Experiment (SORCE) mission. Spectral differences of order 10% have been found between the TSIS-1 SIM and independent solar irradiance reference spectra. The TSIS-1 Hybrid Solar Reference Spectrum (TSIS-1 HSRS) is a new reference spectrum that was developed by normalizing independent high-resolution solar line spectra, measured at lower radiometric accuracy, to the SI- traceable irradiance scale of the TSIS-1 SIM and the CubeSat Compact SIM instruments. Recently, this new solar reference spectrum was extended in wavelength to span the ultraviolet to the longwave infrared (115 nm to 200 microns).

In this study, we utilize the Whole Atmosphere Community Climate Model (WACCM) to investigate the impacts on the modeled atmospheric state (dynamics and composition) resulting from changing the solar forcing dataset from the current NRLSSI2 model (namely, the LASP WHI spectrum with theoretical extension to long wavelengths) to the extended TSIS-1. WACCM is an earth system model with coupled chemistry that extends from the surface into the lower thermosphere. Differences in key constituents in the middle and upper atmosphere such as ozone, hydroxyl and atomic oxygen are presented and related to changes in particular spectral bands. The detectability of these differences in the presence of geophysical variability will be discussed.

CLARREO Pathfinder Uses Solar Calibrations to Obtain Low Uncertainty Reflectance and Radiance Measurements of Earth Scenes

Paul Smith [paul.smith@lasp.colorado.edu]¹, Peter Pilewskie¹, and Greg Kopp¹, Yolanda Shea², Gary Fleming²

Laboratory for Atmospheric and Space Physics, Boulder, CO
NASA Langley Research Center, Hampton, VA

The Climate Absolute Radiance and Refractivity Observatory (CLARREO) Pathfinder mission will measure the Earth reflectance and reflected radiance to obtain a climate record by imaging in the near UV to near IR spectral range (350 – 2300 nm) with its sole instrument, the Hyper Spectral Imager for Climate Science (HySICS). Earth-scene measurements with 0.5-km spatial and 3-nm spectral resolution will achieve an average SI-traceable radiometric uncertainty of 0.3% (1-sigma) in reflectance via an on- orbit solar-calibration approach using direct views of the solar disk to obtain the Sun/Earth reflectance ratio with high accuracy. Comparison with the known, SI- traceable solar spectral irradiance, measured by contemporary instruments such as TSIS-SIM, enable conversions to reflected radiances. The CLARREO Pathfinder will commence one year of operations from the International Space Station in 2024.

Impact of reference solar spectra differences on radiometric cross-calibration of satellite imagers

Raj Bhatt [Rajendra.bhatt@nasa.gov]¹, David Doelling¹,Odele Coddington², Yolanda Shea¹, Peter Pilewskie²,

NASA Langley Research Center, Hampton, VA
LASP / University of Colorado – Boulder, CO

A reference solar spectral irradiance (SSI) dataset is an essential input in satellite ground processing systems to derive L1B radiance datasets from reflectance measurements or vice-versa. The choice of reference SSI spectrum for satellite data processing has constantly changed over the past four decades with the increasing availability of more reliable SSI measurements with extended spectral coverage.

Currently, numerous SSI datasets with noticeable radiometric differences are in use among the multiple satellite operators. This non-uniformity in the usage of reference solar spectra adds extra challenges to achieve radiometric harmonization across the sensors and can potentially lead to incompatible retrievals from the multi-sensor datasets. This paper presents a comprehensive analysis of absolute radiometric comparison between the most widely used SSI datasets and quantifies their impacts in satellite sensor cross-calibration. Our analysis shows that the existing discrepancy in the usage of different reference solar spectra in the L1B processing of the two VIIRS instruments onboard NOAA-20 and SNPP satellite platforms can result in a radiometric inconsistency in their reflective solar bands radiances by up to 3%, regardless of normalizing their reflectance calibrations to a common radiometric scale. This paper also highlights the TSIS-1 Hybrid Solar Reference Spectrum (HSRS), which is a new high-resolution composite solar spectrum developed by normalizing fine spectral resolution solar line observations to the high-accuracy TSIS-1 SIM absolute irradiance measurements. The TSIS-1 HSRS has an unprecedented absolute accuracy of 0.3% between 0.46 and 2.365 μm, 0.5% from 0.4 to 0.46 μm, and 1.3% below 0.4 μm and above 2.365 μm. The CLARREO Pathfinder mission will incorporate the TSIS-1 HSRS SSI dataset in providing high-accuracy hyper-spectral Earth-reflected solar radiances from the SI traceable reflectance measurements to support climate benchmarking and on-orbit absolute radiometric intercalibration.

High-spectral resolutioin SWIR solar reference for Vicarious Calibrations of Space-born GHGs Sensors

Fumie Kataoka [kataoka.fumie@restec.or.jp]¹, Akihiko Kuze², Kei Shiomi², Hiroshi Suto²

Remote Sensing Technology Center of Japan
Japan Aerospace Exploration Agency

In recent years, multiple GHG sensors including GOSAT, GOSAT-2, OCO-2, OCO-3, and TROPOMI, have been launched and compiled a decade-long record of global CO2 and CH4 concentrations. These GHG sensors observe near- infrared and shortwave infrared radiance reflected from the earth’s surface and the atmosphere. To determine the radiometric spectral level and the sensor degradation, the vicarious calibration using radiative transfer calculation is useful as an independent evaluation method (https://www.eorc.jaxa.jp/GOSAT/GHGs_Vical/index.html). We conducted the vicarious calibration evaluation, using well-characterized surface targets Railroad Valley, Nevada (RRV), USA. The key elements to accurate calculation of spectral radiances at the top of the atmosphere (TOA) are the setting of surface reflectance, surface BRDF characteristics, and solar irradiance database. We use a new solar irradiance reference spectrum TSIS-HSRS (The Total and Spectral Solar Irradiance Sensor-1 Hybrid Solar Reference Spectrum).